New improved antibiotics are continually in demand, particularly for the treatment of human diseases. Increased potency, expanded spectrum of bacterial inhibition, increased in vivo efficacy, and improved pharmaceutical properties are some of the goals for improved antibiotics.
Enterococci are important human pathogens. Infections caused by enterococci are generally difficult to treat. Glycopeptides, such as vancomycin and teicoplanin, have become important therapies in the treatment of infections due to enterococci. However, strains of E. faecium and E. faecalis have recently been isolated that are resistant to vancomycin. R. Leclercq et al., "Plasmid Mediated Resistance to Vancomycin and Teicoplanin in Enterococcus Faecium," The New England Journal of Medicine, 319(3), 157-116 (1988) and A. H. C. Uttley et al., "Vancomycin-Resistant Enterococci," Lancet, 1, 57-58 (1988). The isolates were also found to be resistant to other antibiotics.
Glycopeptides, such as vancomycin and teicoplanin, exhibit various degrees of serum protein binding. The level of human serum protein binding for vancomycin and teicoplanin has been reported to be 55% and about 90%, respectively. R. Moellering et al., "Pharmacokinetics of Vancomycin in Normal Subjects and in Patients with Reduced Renal Function," Reviews of Infectious Disease, 3, (Supp.), S230-S235 (1981) and A. Assandri and A. Bernareggi, "Binding of Teicoplanin to Human Serum Albumin," Eur. J. Clinical Pharmacol., 33, 191-195 (1987). The percentage of serum protein binding exhibited by teicoplanin is considered to be a high level of binding; however, the level of serum protein binding exhibited by vancomycin is relatively low. The free or unbound form of the antibiotic is the form that. participates in the biological activity. Therefore, the binding of the antibiotics to serum proteins affects the pharmaceutical properties of the antibiotic.
In the search for new antibiotics, structural modification of known antibiotics is attempted whenever possible. The glycopeptide antibiotics have such complex structures that even small changes are difficult. Furthermore, it is difficult to predict the effect these changes will make in the antimicrobial and physiological properties. Processes for modifying known antibiotics and the new active derivatives made by such processes, therefore, continue to be of great importance.
Previously, N-alkyl and N-acyl derivatives of the glycopeptides vancomycin, A51568A, A51568B, M43A and M43D have been prepared (U.S. Pat. Nos. 4,639,433; 4,643,987; and 4,698,327). Several of these compounds exhibited microbiological activity against vancomycin-resistant isolates. T. Nicas et al., Antimicrobial Agents and Chemotherapy, 33(9), 1477-1481 (1989).
The formula I compounds are new members of the glycopeptide group of antibiotics. These new compounds are N-alkyl and N-acyl derivatives of the known A82846 glycopeptides, factors A, B, and C (EPO 265,071 A1), and PA-42867-A (EPO 231,111 A2). Representative formula I compounds exhibited antimicrobial activity against vancomycin-resistant isolates. Also, the new compounds are not as highly serum protein bound as other glycopeptides. The level of serum protein binding for the formula I compounds is similar to that exhibited by vancomycin. This level is much lower than that of other highly potent glycopeptides, such as teicoplanin.